Re: [PATCH v5 3/5] selftests/mm: reimplement is_backed_by_thp() with more precise check

[Zi Yan]

On 19 Aug 2025, at 4:54, David Hildenbrand wrote:

> On 18.08.25 20:46, Zi Yan wrote:
>> and rename it to is_backed_by_folio().
>>
>> is_backed_by_folio() checks if the given vaddr is backed a folio with
>> a given order. It does so by:
>> 1. getting the pfn of the vaddr;
>> 2. checking kpageflags of the pfn;
>>
>> if order is greater than 0:
>> 3. checking kpageflags of the head pfn;
>> 4. checking kpageflags of all tail pfns.
>>
>> pmd_order is added to split_huge_page_test.c and replaces max_order.
>>
>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
>> Reviewed-by: Wei Yang <richard.weiyang@xxxxxxxxx>
>> Reviewed-by: wang lian <lianux.mm@xxxxxxxxx>
>> ---
>>   .../selftests/mm/split_huge_page_test.c       | 88 ++++++++++++++-----
>>   tools/testing/selftests/mm/vm_util.c          | 13 +++
>>   tools/testing/selftests/mm/vm_util.h          |  4 +
>>   3 files changed, 81 insertions(+), 24 deletions(-)
>>
>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>> index 089e146efeab..56d1eaf9a860 100644
>> --- a/tools/testing/selftests/mm/split_huge_page_test.c
>> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
>> @@ -25,6 +25,7 @@
>>   uint64_t pagesize;
>>   unsigned int pageshift;
>>   uint64_t pmd_pagesize;
>> +unsigned int pmd_order;
>>    #define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages"
>>   #define SMAP_PATH "/proc/self/smaps"
>> @@ -34,26 +35,66 @@ uint64_t pmd_pagesize;
>>   #define PID_FMT_OFFSET "%d,0x%lx,0x%lx,%d,%d"
>>   #define PATH_FMT "%s,0x%lx,0x%lx,%d"
>>  -#define PFN_MASK     ((1UL<<55)-1)
>> -#define KPF_THP      (1UL<<22)
>> -
>> -static int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
>> +static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
>> +		int kpageflags_fd)
>>   {
>> -	uint64_t paddr;
>> -	uint64_t page_flags;
>> +	unsigned long pfn_head;
>> +	uint64_t pfn_flags;
>> +	unsigned long pfn;
>> +	unsigned long i;
>
> Final nit (sorry!) :)
>
> const unsigned long nr_pages = 1ul << order;
>
> so you can make some of the code below easier to read.

Sure. Will send a fixup.

>
> Acked-by: David Hildenbrand <david@xxxxxxxxxx>
>
Thanks.


--
Best Regards,
Yan, Zi